ozankabak commented on code in PR #11506:
URL: https://github.com/apache/datafusion/pull/11506#discussion_r1687127355
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datafusion/physical-expr-common/src/physical_expr.rs:
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@@ -191,6 +193,33 @@ pub fn with_new_children_if_necessary(
}
}
+/// Rewrites an expression according to new schema; i.e. changes the columns it
+/// refers to with the column at corresponding index in the new schema. Returns
+/// an error if the given schema has fewer columns than the original schema.
+/// Note that the resulting expression may not be valid if data types in the
+/// new schema is incompatible with expression nodes.
+pub fn with_new_schema(
+ expr: Arc<dyn PhysicalExpr>,
+ schema: &SchemaRef,
+) -> Result<Arc<dyn PhysicalExpr>> {
+ Ok(expr
+ .transform_up(|expr| {
+ if let Some(col) = expr.as_any().downcast_ref::<Column>() {
+ let idx = col.index();
+ let Some(field) = schema.fields().get(idx) else {
+ return plan_err!(
Review Comment:
This function can be called (in theory) by any compatible superset schema.
If the caller gives a schema that is narrower, it is surely and error (as the
return value reflects). Since the error is triggerred by a bad argument, and
the function is called during planning time, we decided to go with `plan_err`.
I will add an entry in my notes to revisit this in the future -- if it turns
out this error is surely indicative of a bug in all use cases, we should change
it to `internal_err`.
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